Percutaneous angioplasty using medical balloon catheters has been widely used for dilation therapy of stenoses or blocked portions of vascular cavities and for restoration or improvement of blood flow in coronary artery, peripheral blood vessels, and the like. In a typical medical balloon catheter, a balloon that can be inflated or contracted by internal pressure adjustment is joined to the distal end portion of a catheter shaft, and an inner cavity (guidewire lumen) for passing a guidewire and an inner cavity (inflation lumen) for supplying a pressure fluid for internal pressure adjustment in the balloon are provided in the longitudinal direction of the catheter shaft inside thereof.
A typical example of PTCA technique using such a medical balloon catheter is described below. First, a guide catheter is inserted from the punctured zone into a large femoral artery, brachial artery, scapular artery, and the like, and the distal end thereof is disposed in the inlet of a coronary artery via the main artery. The guidewire inserted into the guidewire lumen is then advanced through the stenotic zone, and medical balloon catheter is inserted along the guidewire, and positioned in the stenosis. A pressure fluid is then supplied to the balloon via the inflation lumen by using an indeflator or the like, and dilatotherapy of the stenosis is conducted by inflating the balloon. After the dilatotherapy of the stenosis, PTCA is completed by contracting the balloon by pressure reduction and pulling it out of the body. In the present example of technique, usage of the medical balloon catheter for PTCA in coronary artery stenosis was described, but the medical balloon catheters have been also widely employed for dilatotherapy in body cavities and other vascular cavities such as peripheral vascular cavities.
Such a medical balloon catheter has a structure in which a balloon 2 is joined to the distal end of a catheter shaft 1, and a hub 3 for supplying a pressure fluid for adjusting internal pressure in the balloon is joined to the catheter shaft 1. Based on the structure of catheter shaft 1, the catheters can be classified into two types.
The first type is the over-the-wire type (OTW type) in which the guidewire lumen 4 is provided from the proximal end side to the distal end side of the medical balloon catheter, that is, over the entire length of the medical balloon catheter and a guidewire port is provided in the hub 3 (FIG. 1). The second type is the rapid exchange type (RX type) in which the guidewire lumen is provided on the distal end side of the medical balloon catheter, and the guidewire port 5 is provided in the middle part of catheter shaft 1 (FIG. 2).
A variety of characteristics are required from medical balloon catheters. The main among them can be generally classified into the following three groups: the ability to pass through the stenotic zone (crossability), the ability to follow the curved blood vessel (trackability), and the ability to transmit a force when the medical balloon catheter is inserted into a blood vessel (pushability). Kink resistance is an example of a characteristic relating to pushability.
Reducing the profile (thickness) of catheter shaft improves crossability, but tends to degrade pushability and kink resistance. Further, increasing rigidity of catheter shaft improves pushability and kink resistance, but tends to degrade crossability. In other words, all the above-mentioned characteristics are closely related to each other, and it is not easy to improve all the characteristics at the same time. Accordingly, a variety of techniques for improving crossability, pushability and trackability and increasing kink resistance have been disclosed.
Examined Japanese Patent Application No. 5-28634 (Catheter) discloses a rapid exchange medical balloon catheter, in which an opening of the guidewire lumen is provided in the joining region of a medium portion (distal end shaft in accordance with the present invention) and a base portion (proximal end shaft in accordance with the present invention) and when the guidewire is contained in the guidewire lumen, the catheter receives a continuous longitudinal support over the entire length thereof.
Such prior art technology makes it possible to increase kink resistance in a state in which the guidewire is contained in the catheter, that is, inside the guide catheter. The drawback of that technology was that when the guidewire was inserted, the catheter could be easily bent in the joining region of the medium portion and base portion and operation ability by the operator was very poor.
Japanese Patent No. 2933389 (Balloon Catheter Comprising Inner Cavity for Guidewire on the Distal End Side) discloses a medical balloon catheter in which a transition portion extending from the distal end side of the opening of the proximal end inner cavity of the guidewire lumen to the vicinity of the distal end of the first shaft portion (proximal end shaft in accordance with the present invention) has a rigidity between that of the first shaft portion and second shaft portion (distal end shaft in accordance with the present invention).
This prior art technology provides a catheter shaft with increased kink resistance, but this increase in kink resistance is implemented by additionally providing the second shaft with a coil-like member as a deformation preventing structure. The problem associated with such additional coil-like member was that the number of operations during catheter manufacture was greatly increased and, at the same time, the assembly method was made difficult which resulted in the increased production cost. Further, with this prior art technology, the deformation preventing structure was mounted on the outer or inner side of the outer sleeve, or on the outer side of a core tube. When the deformation preventing structure was mounted on the outer side of the outer sleeve, the increase in the outer diameter of the outer sleeve could degrade crossability, and when the deformation preventing structure was mounted on the inner side of the outer sleeve or on the outer side of the cure tube, the inflation lumen was locally narrowed, producing an adverse effect on dilation or contraction behavior of the balloon.
Further, Japanese Patent Publication No. 6-507105 (Vascular Catheter Comprising Guidewire Proximal End Cavity and Intermediate Member” discloses a vascular catheter comprising a main shaft (proximal end shaft in accordance with the present invention), a balloon, a plastic shaft portion (distal end shaft in accordance with the present invention) located between the main shaft and the balloon, an intermediate member mounted on the main shaft, extending inside the plastic shaft portion in the distal end direction and having a rigidity not higher than that of the main shaft portion, and a guidewire lumen, wherein the guidewire inlet is withdrawn from the distal end of the main shaft portion in the proximal end direction.
Such prior art technology provides a vascular catheter with improved pushability and trackability and also increased kink resistance. However, kink resistance demonstrated when the vascular catheter is inserted into the guide catheter along the guidewire can hardly be considered good. In order to further increase kink resistance, it is necessary to enlarge the diameter of the core wire used as a non-rigid intermediate member. However, in order to ensure the effective inflation lumen, the increase in the profile of the catheter shaft is required, and the decrease in crossability and trackability causes concerns.
Examined Japanese Patent Application No. 4-44553 (Catheter Equipped with Balloon) discloses a catheter equipped with a balloon comprising a rigidity increasing member which extends in the axial direction in the outer tube and provides it with rigidity and a portion comprising no such rigidity increasing member at the distal end of he outer tube.
On the other hand, a balloon catheter is used to conduct dilatotherapy mainly by inserting the catheter into the body passage which is the object of therapy and introducing the internal pressure into the therapy zone. Therefore, the required mechanical properties include a strength sufficient to prevent rupture of the balloon when a pressure necessary for the dilation is introduced and a capability to control the balloon safely to the desired dilation size. Furthermore, in most cases, in order to conduct therapy in a vascular system, the catheter has to be inserted to the zone of pathology changes and prescribed position along the blood vessel and the operation ability of the distal end portion of the catheter for such an insertion is very important.
The catheter is typically composed of thin tubular members and has to be passed through the curved zones inside the body or narrow stenotic zones by operating the catheter from outside of the body through the insertion opening into the body. Accordingly, a small size of the catheter itself, in particular, of the distal end thereof is very important. In addition, a force applied to the catheter from outside of the body has to be effectively transmitted to the distal end portion and flexibility is required to adapt to the cured portions. Further, because guidewire is usually used by being passed inside the catheter, a small friction resistance between the catheter and guidewire is also an important property allowing for smooth movement of the catheter without disrupting the force transmission. In order to obtain such an operation ability, the structure of a typical balloon catheter is required to have the following properties: (1) flexibility of the distal end (far end) portion allowing the catheter to follow the curved internal passages, (2) strength of the proximal end (near end) portion sufficient to provide for good transmission of force to the distal end, and (3) low friction and high sliding ability of the tube used for passing a guidewire in order to suppress friction resistance. Catheters satisfying those requirements are most often made of polyethylene, high-strength polyamide, or high-strength polyamide elastomers.
With respect to thinness and flexibility, a small size and flexibility of the balloon portion at the distal end of the catheter and in the vicinity thereof are the especially important properties. Furthermore, because this portion is often inserted into the curved portions or slides over the softest portion of the guidewire inserted therein, the absence of discontinuity in this flexibility is also required. Thus, when the catheter is disposed in a curved portion, if the flexibility is discontinuous, bending of the catheter becomes discontinuous, and guidewire resistance in this portion greatly increases causing degradation of operation ability.
Further, a fixed portion of the tube for passing the balloon and guidewire is typically present as the distalmost portion “tip” at the de of balloon catheter. When this tip portion is hard, the difference in flexibility with the guidewire let out of the tip increases and guidewire can be easily bent in this zone, becoming a serious cause of operation ability degradation. Furthermore, in case of zone of pathological changes with advanced calcification, the following effects are of frequent occurrence. Thus, when an attempt is made to pass a balloon catheter along the guidewire that has been passed through such a zone, if the distal end is not sufficiently thin, it is obstructed by the hard zone of pathological changes and is not able to pass therethrough, or if the tip portion is hard, it is caught by the hard zone of pathological changes and is not able to pass therethrough.
Furthermore, in recent years, metallic stationary dilators typically called stents are often used in vascular dilation therapy. In order to conduct shape dilation after stent dilation (post-dilation) and also in case of re-stenosis inside the stents and stenosis at the distal end side of the stents, the balloon catheter has to be passed inside the stents. However, in such a case, similarly to the zones of pathological changes with advanced calcification, the problem was that if the distal end was not sufficiently small and the tip portion was hard, the catheter was caught by the metallic stent and could not pass therethrough.